Japanese patent publication 2006-095526A discloses a method in which water is recovered from wastewater originating in a confined space by pervaporation. However, wastewater such as urine and domestic wastewater usually contains volatile components such as ammonia, and the volatile components may be disadvantageously mixed in the recovered water. Furthermore, when the wastewater contains a hardness component, scale trouble is caused on a pervaporation membrane. When the wastewater contains an organic substance such as protein, fouling may occur, which deteriorates membrane distillation capability. In addition, pervaporation requires high energy consumption.
Japanese Patent Publication 2010-119963A discloses a method in which wastewater originating in a confined space is subjected to a biological treatment, membrane separation, and subsequently distillation or freezing in order to recover water. However, in a biological treatment, microorganisms are likely to be inactivated when operating conditions thereof deviate from the norm. Inactivated microorganisms are not reactivated again. Moreover, in an activated sludge process, one third to half the organic substance is removed in the form of sludge. That is, an activated sludge process produces sludge containing precious water as a waste substance.